On Tuesday, Danish intelligence chief Finn Borch Andersen confirmed the measures had been taken to prevent the alleged plot.

Image copyrightEPAImage caption
The bridge between the Danish islands of Zealand and Funen was also closed by police

The alleged target was meant to be a senior member of the Arab Struggle Movement for the Liberation of Ahvaz (ASMLA), Mr Andersen said. The group seeks a separate state for ethnic Arabs in a region of western Iran.

That attack was claimed by a different Arab separatist group and the Islamic State group, although neither offered proof of their claims.

What has the response been?

An Iranian foreign ministry spokesman said such "biased reports" and allegations pursued "the enemy's plots and conspiracies" to harm the developing relations between Iran and Europe, according to Tasnim news agency.

Mr Rasmussen said, after a meeting with his British counterpart Theresa May in Oslo, that he appreciated her support.

"In close collaboration with UK and other countries we will stand up to Iran," he tweeted.

Foreign Minister Anders Samuelsen said Denmark would discuss further actions with European partners in the coming days.